Microphone



Nov. 25, 1958 M. BONNAFFOUS MICROPHONE Filed July 7, 1954 BONNAFFOUS INVENTOR.

MAURIJCE 7 g Q 5. H F 5 m M 9 3 F O 3 m 4 A 7 0 0 3 3 0 0 4 1 on. 0 0 o 0 w m n 0 0 0 0 OOOMO 6 a o 0 \IIE E AG ENT United States Patent MICROPHONE Maurice Bonnalfous, Paris, France, assignor to Societe dAppareillage et dExploitation des Etablissements Ponsot, in short Socapex-Ponsot, Suresnes, France, a corporation of France Application July 7, 1954, Serial No. 441,891

Claims priority, application France July 10, 1953 Claims. (Cl. 179121) My invention relates to improvements in microphones and it covers more particularly microphones of the socalled differential type. It should be remembered that, in a differential microphone, the diaphragm is subjected, on either side, to the action of surrounding noise whereby the effects of this latter on both sides of the microphone balance each other and consequently the transmission of actual speech is favored.

Now, my invention has for its object a microphone adapted to operate differentially or otherwise as required by the user.

A further object of my invention consists in producing such a microphone wherein the sensitivity to surrounding noise may be adjusted within a range between zero and a maximum value.

My invention has also for its object the provision of such a microphone which, under conditions otherwise equal, is lighter than any known microphone and which in particular, for a predetermined weight, produces at the output end a very high signal voltage.

My invention has also for its object a microphone of the type referred to which is of an easy and economical execution. According to my invention, the openings formed in the microphone for the admission of the surrounding noises may be covered partly or wholly.

According to my invention, embodiments are provided which include a cylindrical member provided with perforations the operative area of which is controlled by a rotary sleeve cooperating with said cylindrical member and provided with openings which are similar to those of said sleeve.

According to a preferred embodiment, the said cylindrical member is constituted by the cylindrical spacing member generally provided in differential microphones.

According to a further embodiment, the perforations are formed in a fiat surface and their cross-sectional area is adjusted in association with a ring-shaped member cooperating with the said surface and provided with similar perforations.

According to a still further embodiment, the cooperating perforations are formed in two frustoconical diaphragms engaging together the vibratory plate of the microphone. I will now describe by way of example various embodiments of my invention, reference being made .to accompanying drawings wherein:

Fig. 1 is a sectional view of a microphone according to my invention;

Fig. 2 is a corresponding front view thereof;

Fig. 3 is a perspective view of the perforated cylindrical member, part of which is torn off;

Fig. 4 is a perspective view of a screen a part of which is torn off;

Fig. 5 is a perspective view of a spacing member, a part of which is likewise torn off;

Fig. 6 is a diagrammatic perspective view of the electromagnetic system and vibratory plate of the microphone; and

2,862,070 Patented Nov. 25, 1958 Fig. 7 is a perspective View of a ring forming part of my improved microphone.

In Figs. 1 and 2, the body 20 of the microphone made, for instance, of plastic material includes a handle 21 at its lower end while its upper end carries the capsule. The front surface 23 of the microphone is provided with a large annular opening 24 inside which is housed a ring 25 provided with regularly distributed perforations 26. The inner surface of the said ring, which is provided for this purpose with a groove 27, is engaged by the front surface 28 of a cylindrical member 29 (Fig. 3). The said front surface or inner flange 28 of the member 29 serves as a bearing for a generally frustoconical screen 30 (Figs. 1 and 4) provided with a peripheral outer flange 31 adapted to engage the said flange 28. The central section 32 at the apex of the said screen may be flat. The screen 30 is provided in the usual manner with numerous perforations 33 and is held in position by a cylindical spacing member or sleeve 34 (Figs. 1 to 5) including a body 35 and an inturned terminal flange 36. The outer edge 37 of the said spacing member engages the outer flange 38 of a capsule which in the example illustrated includes a diaphragm 39 (Fig. 6); the electromagnetic system associated with the said capsule, supported on a disk 50, has been illustrated diagrammatically at 40. A split ring 41 (Fig. 7) is fitted inside the cylindrical member 29 so as to hold the said capsule in position.

According to my invention, the cylindrical member 29 is provided with a plurality of uniformly distributed perforations and is adapted to revolve with reference to the cooperating sleeve 34 also provided with perforations, the distribution of the perforations in the member 29 and in the sleeve 34 being similar. Thus, sleeve 34 acts as a barrier to sound waves wherever its perforations are blocked by the solid portions of cylinder 29.

It Will be assumed for instance that the cylindrical member 29 is provided with circular perforations 42 distributed in horizontal or vertical rows in staggered formation, if required, while the sleeve or spacing member 34 is provided with circular openings 43 the diameter of which is the same as that of the perforations 42, the perforations 42 and 43 being distributed in an identical man'- ner.

The angular setting of the sleeve or spacing member 34 with reference to the cylinder 29 can be manually varied by suitable means not shown.

The operation of the microphone is as follows: when the relative angular settings of the cylinder 29 and of the sleeve 34 are such that the perforations 43 register exactly with the perforations 42, the microphone operates in the manner of an ordinary differentially-operating microphone, the background noises reaching, via apertures 26, the annular round chamber surrounding cylinder 29 and entering the acoustic chamber containing the microphone capsule through the said superposed perforations, thus exerting their action on both sides of the diaphragm 39.

In contradistinction, if the relative positions of the cylinder 29 and of the sleeve 34 are such that the perforations 42 are no longer in register with the perforations 43, the microphone acts no longer in a differential manner and the sounds constituted, on one hand, by the speech of the user and, on the other hand, by noise all impinge on only one surface of the diaphragm, to wit its outer surface. For all intermediate positions of the cylinder 29 with reference to the sleeve 34, the microphone acts in a more or less marked differential manner.

Such a microphone is of particular advantage in arrangements including earphones allowing the user to listen to his own voice. The user may thus adjust at any 3 moment the differential character of the microphone until optimum audition is obtained, which optimum audition corresponds to optimum transmission at a distance.

A similar effect may be obtained by providing an angularly shiftable perforated ring in register with the ring 25.

According to another embodiment, two frustoconical diaphragmsmay be used.

What I claimis:

l. A microphone comprising a casing with a front wall having a perforated central portion as well as a perforated peripheral portion, a membrane positioned in said casing back of said central portion and forming the forward boundary of a rear chamber within said casing, a per forated barrier member interposed in the path of sound Waves between said rear chamber and said perforated peripheral portion, a blocking member co-opcrating with said barrier member and adapted selectively to obstruct the perforations thereof, and electro-acoustic transducer means coupled with said membrane for translating vibrations of the latter into electric currents.

2. In a microphone, in combination, a casing, a conical microphonic diaphragm positioned in said casing near the forward en'd thereof and having its apex directed toward the interior of the casing, said casing comprising a wall portion having an aperture in line with said diaphragm, a perforated cylindrical sleeve substantially caXial with said conical diaphragm in said casing, means including said sleeve and the rear face of said diaphragm forming anacoustic rear chamber within said casing, a perforated blocking cylinder concentrically positioned in contact with said perforated sleeve and movable with re spect thereto for selectively obstructing the perforations of the latter, means including said casing forming around said sleeve an annular sound chamber open toward the atmosphere, said sound chamber communicating with said rear chamber by Way of said perforations, and electroacoustic transducer means coupled with said membrane for translating vibrations of the latter into electric currents.

3. The combination according to claim 2, further including a perforated cone fitting inside the concavity of said conical diaphragm and positioned between the latter and said wall portion.

4. A microphone comprising a casing with a front wall having a perforated central screen-portion and aperforated annular rim surrounding said screen portion, a perforated cylindrical sleeve in said casing substantially coaxial with said screen portion and of the same diameter as the latter, a perforated cylindrical blocking member concentrically positioned in contact with said sleeve and displaceable with respect thereto for selectively obstructing the perforations thereof, a conical diaphragm disposed inside said sleeve coaxially with said screen portion and turning its concave side toward same, electroacoustic transducer means including a disk member back of said diaphragm, said disk member spanning said sleeve and forming therewith an acoustic chamber around the convex. side-of said diaphragm, and coupling means mechanically linking. the apex of said diaphragm with said disk member.

5. A noise-canceling microphone responsive to pressure differentials, comprising a cylindrical sleeve, apressuresensitive element mechanically independent from said sleeve and positioned within the latter, said element having a front and a rear face, electro-a'coustic transducer means controlled by said pressure-sensitive element for translating vibrations thereof due to impinging sound waves into electric currents, said sleeve being provided with lateral perforations enabling said element to respond to phase differences of said sound waves impinging thereon from opposite sides, and a cylindrical shell concentric with said sleeve and rotatable with respect thereto, said shell being provided with side apertures dimensioned for selectively facilitating or impeding the access of said sound waves to a face of said element.

References Cited in the file of this patent UNITED STATES PATENTS 2,196,342 Ruttenberg Apr. 9,1940 2,301,638 Olson ..t. Nov. 10, 1942 2,512,467 Olson et al. June 20, 1950 2,699,473 Kettler et al. Jan. 11-, 1955' 2,763,730 Paull et al Sept. 18, 1956 2,787,671 Grosskopf et al. Apr. 2, 1957 

